[time-nuts] spectracom line taps

John Ackermann N8UR jra at febo.com
Mon Feb 18 12:37:08 EST 2008

James R. Gorr said the following on 02/18/2008 12:18 PM:
> I have a Spectracom 8140 frequency distribution amp. 
> I see on ebay there are line taps for this device.  Do
> I need the line taps?  Or can I just use the 8140 as
> is?  What are the line taps supposed to do?

I use the 8140T line taps without an 8140 unit.  All they require is a
+12V DC signal riding along with the 10 MHz sine wave.  You can string a
bunch of taps off one reasonably strong source.

I have an HP 5065A Rb that I slightly modified to tap the 10 MHz off
from the internal 10811A oscillator before the divide-by-2 circuit*, and
putting a 12 volt DC bias on the signal (with an isolating capacitor to
protect the rest of the 5065A from the DC, of course).  I feed about 10
of the 8140T taps from this line, and it works well.

The 8140T amps have only decent phase noise performance; I wouldn't use
one for a demanding application, but this string running around the lab
makes it awfully convenient to grab a 10 MHz source wherever I need one.

One thing -- you want to put a DC-isolated 50 ohm load at the end of the
string to terminate the line.  I believe the 8140 amp unit has a fault
detector that will trip if it doesn't see that load, and it's good
practice to properly terminate the line, anyway.


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